Heat dissipation structure

ABSTRACT

A heat dissipation structure includes a substrate, an electronic component mounted on the substrate, a heat dissipation member for dissipating heat generated from the electronic component, and a thermal conductive adhesive sheet provided on the substrate so as to cover the electronic component. The thermal conductive adhesive sheet includes a thermal conductive layer containing a plate-like boron nitride particle. The thermal conductive layer has a thermal conductivity in a direction perpendicular to the thickness direction of the thermal conductive layer of 4 W/m·K or more, and the thermal conductive adhesive sheet is in contact with the heat dissipation member.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Applications No. 2010-018256 filed on Jan. 29, 2010; No. 2010-090908 filed on Apr. 9, 2010; No. 2010-161845 filed on Jul. 16, 2010; No. 2010-161850 filed on Jul. 16, 2010; and No. 2010-172325 filed on Jul. 30, 2010, the contents of which are hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat dissipation structure.

2. Description of Related Art

As a capacity of electronic components such as a memory has been increasing in these days, an amount of heat generation at the time of operation has been increasing. The heat may cause deterioration of the electronic components, and therefore in electronic components and structures including a substrate on which such electronic components are mounted, high heat dissipation (high thermal conductivity) is required.

For example, a structure has been proposed (e.g., see a memory heatsink (heatspreader), Internet (URL: http://www.ainex.jp/products/hm-02.htm)). In this structure, a flat-plate memory heatsink made of aluminum is placed on the top face of a plurality of memories mounted on a substrate; and the substrate, the memories, and the memory heatsink are sandwiched with a clip.

In such a structure of memory heatsink, Internet, the memory heatsink is brought in contact with the top face of the memory, thereby allowing the memory heatsink to dissipate heat generated from the memory.

SUMMARY OF THE INVENTION

However, in such a memory heatsink, Internet, the side face of the memory is not in contact with the flat-plate memory heatsink, and moreover, when the thicknesses of the memories vary, a gap is created between the top face of the memory having a small thickness and the memory heatsink. Therefore, there is a disadvantage in that the heat generated from the memory cannot be dissipated sufficiently.

An object of the present invention is to provide a heat dissipation structure with excellent heat dissipation.

A heat dissipation structure of the present invention includes a substrate, an electronic component mounted on the substrate, a heat dissipation member for dissipating heat generated from the electronic component, and a thermal conductive adhesive sheet provided on the substrate so as to cover the electronic component, wherein the thermal conductive adhesive sheet includes a thermal conductive layer containing a plate-like boron nitride particle, the thermal conductive layer has a thermal conductivity in a direction perpendicular to the thickness direction of the thermal conductive layer of 4 W/m·K or more, and the thermal conductive adhesive sheet is in contact with the heat dissipation member.

In the heat dissipation structure of the present invention, it is preferable that the thermal conductive adhesive sheet includes an adhesive layer or a pressure-sensitive adhesive layer laminated onto at least one face of the thermal conductive layer, and the adhesive layer or the pressure-sensitive adhesive layer is adhered to or pressure-sensitively adhered to the substrate.

In the heat dissipation structure of the present invention, the electronic components are covered with the thermal conductive adhesive sheet, and therefore heat generated from the electronic components is conducted from the top face and the side face of the electronic components to the thermal conductive adhesive sheet. Then, the heat is conducted from the thermal conductive adhesive sheet to the heat dissipation member, and the heat is dissipated to outside at the heat dissipation member.

Therefore, heat generated from the electronic components can be efficiently dissipated by the thermal conductive adhesive sheet and the heat dissipation member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of an embodiment of a heat dissipation structure of the present invention.

FIG. 2 is a process drawing for describing a method for producing a thermal conductive layer,

(a) illustrating a step of hot pressing a mixture or a laminated sheet,

(b) illustrating a step of dividing the pressed sheet into a plurality of pieces, and

(c) illustrating a step of laminating the divided sheets.

FIG. 3 shows a perspective view of a thermal conductive layer.

FIG. 4 shows a cross-sectional view of a thermal conductive adhesive sheet.

FIG. 5 is a process drawing for describing production of the heat dissipation structure of FIG. 1, and shows a step of fixing a substrate on which electronic components are mounted to a housing that supports a frame, and preparing a thermal conductive adhesive sheet.

FIG. 6 shows a cross-sectional view of another embodiment of the heat dissipation structure of the present invention (embodiment in which the thermal conductive adhesive sheet is composed of a thermal conductive layer).

FIG. 7 shows a process drawing for describing production of the heat dissipation structure of FIG. 6, and shows a step of fixing a substrate on which electronic components are mounted to a housing that supports a frame, and preparing a thermal conductive adhesive sheet.

FIG. 8 shows a cross-sectional view of another embodiment (embodiment in which the other end portion of the thermal conductive adhesive sheet is in contact with the housing) of the heat dissipation structure of the present invention.

FIG. 9 shows a cross-sectional view of another embodiment (embodiment in which an adhesive/pressure-sensitive adhesive layer is in contact with the top face of the electronic components) of the heat dissipation structure of the present invention.

FIG. 10 shows a perspective view of a test device (Type I, before bend test) of a bend test.

FIG. 11 shows a perspective view of a test device (Type I, during bend test) of a bend test.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a cross-sectional view of an embodiment of a heat dissipation structure of the present invention, FIG. 2 shows a process drawing for describing a method for producing a thermal conductive layer, FIG. 3 shows a perspective view of a thermal conductive layer, FIG. 4 shows a cross-sectional view of a thermal conductive adhesive sheet, and FIG. 5 shows a process drawing for describing production of the heat dissipation structure of FIG. 1.

In FIG. 1, a heat dissipation structure 1 includes a substrate 2, electronic components 3 mounted on the substrate 2, a frame 4 as a heat dissipation member for dissipating heat (heat transportation, heat conduction) generated from the electronic components 3, and a thermal conductive adhesive sheet 5 provided on the substrate 2.

The substrate 2 is formed into a generally flat-plate shape, and is formed from, for example, ceramics such as aluminum nitride and aluminum oxide; for example, glass/epoxy resin; and for example, synthetic resins such as polyimide, polyamide-imide, acrylic resin, polyether nitrile, polyether sulfone, polyethylene terephthalate, polyethylene naphthalate, and polyvinyl chloride.

The electronic components 3 include, for example, an IC (integrated circuit) chip 20, a condenser 21, a coil 22, and/or a resistor 23. The electronic components 3 control, for example, a voltage of below 5 V, and/or an electric current of below 1 A. The electronic components 3 are mounted on the top face of the substrate 2, and are disposed with a space provided therebetween in the plane direction (plane direction of the substrate 2, left and right directions and depth direction in FIG. 1). The electronic components 3 have a thickness of, for example, about 1 μm to 1 cm.

The frame 4 is supported by a housing (not shown in FIG. 1) accommodating the substrate 2, and is disposed at an outer side (lateral side) of the substrate 2 with a space provided therebetween. The frame 4 is formed into a generally frame shape surrounding the substrate 2 when viewed from the top. The frame 4 is formed into a generally rectangular shape extending in up-down directions when viewed in cross section. The frame 4 is formed from, for example, metals such as aluminum, stainless steel, copper, or iron.

The thermal conductive adhesive sheet 5 is provided on the substrate 2 so as to cover the electronic components 3. The thermal conductive adhesive sheet 5 is disposed so that one end portion (right end portion in FIG. 1) of the thermal conductive adhesive sheet 5 is in contact with the surface (top face and side face) of the electronic components 3, and the other end portion (upper left end portion in FIG. 1) of the thermal conductive adhesive sheet 5 is in contact with the inner face (right side face) of the frame 4.

To be specific, in the heat dissipation structure 1, the thermal conductive adhesive sheet 5 is generally L-shaped when viewed in cross section; disposed so that the center (center in left and right directions) portion and one end portion thereof extend in the plane direction on the top face of the substrate 2; and disposed so that a portion of the other end side from the center portion thereof is bent upward from the one end edge (left end edge) of the substrate 2, and the other end portion of the thermal conductive adhesive sheet 5 extends upward at the right side face (inner face) of the frame 4.

The thermal conductive adhesive sheet 5 includes, as shown in FIG. 4, a thermal conductive layer 6, and an adhesive layer 7 or a pressure-sensitive adhesive layer 7 (in the following, they are sometimes generally called “adhesive/pressure-sensitive adhesive layer 7”) laminated on the back face (bottom face) of the thermal conductive layer 6.

The thermal conductive layer 6 is formed into a sheet form, and contains boron nitride particles.

To be specific, the thermal conductive layer 6 contains boron nitride (BN) particles as an essential component, and further contains, for example, a resin component.

The boron nitride particles are formed into a plate (or flakes), and are dispersed in a manner such that the boron nitride particles are oriented in a predetermined direction (described later) in the thermal conductive layer 6.

The boron nitride particles have an average length in the longitudinal direction (maximum length in the direction perpendicular to the plate thickness direction) of, for example, 1 to 100 μm, or preferably 3 to 90 μm. The boron nitride particles have an average length in the longitudinal direction of, 5 μm or more, preferably 10 μm or more, more preferably 20 μm or more, even more preferably 30 μm or more, or most preferably 40 μm or more, and usually has an average length in the longitudinal direction of, for example, 100 μm or less, or preferably 90 μm or less.

The average thickness (the length in the thickness direction of the plate, that is, the length in the short-side direction of the particles) of the boron nitride particles is, for example, 0.01 to 20 μm, or preferably 0.1 to 15 μm.

The aspect ratio (length in the longitudinal direction/thickness) of the boron nitride particles is, for example, 2 to 10000, or preferably 10 to 5000.

The average particle size of the boron nitride particles as measured by a light scattering method is, for example, 5 μm or more, preferably 10 μm or more, more preferably 20 μm or more, particularly preferably 30 μm or more, or most preferably 40 μm or more, and usually is 100 μm or less.

The average particle size as measured by the light scattering method is a volume average particle size measured with a dynamic light scattering type particle size distribution analyzer.

When the average particle size of the boron nitride particles as measured by the light scattering method is below the above-described range, the thermal conductive layer 6 may become fragile, and handleability may be reduced.

The bulk density (JIS K 5101, apparent density) of the boron nitride particles is, for example, 0.3 to 1.5 g/cm³, or preferably 0.5 to 1.0 g/cm³.

As the boron nitride particles, a commercially available product or processed goods thereof can be used. Examples of commercially available products of the boron nitride particles include the “PT” series (e.g., “PT-110”) manufactured by Momentive Performance Materials Inc., and the “SHOBN®UHP” series (e.g., “SHOBN®UHP-1”) manufactured by Showa Denko K.K.

The resin component is a component that is capable of dispersing the boron nitride particles, i.e., a dispersion medium (matrix) in which the boron nitride particles are dispersed, including, for example, resin components such as a thermosetting resin component and a thermoplastic resin component.

Examples of the thermosetting resin component include epoxy resin, thermosetting polyimide, phenol resin, urea resin, melamine resin, unsaturated polyester resin, diallyl phthalate resin, silicone resin, and thermosetting urethane resin.

Examples of the thermoplastic resin component include polyolefin (e.g., polyethylene, polypropylene, and ethylene-propylene copolymer), acrylic resin (e.g., polymethyl methacrylate), polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide, polycarbonate, polyacetal, polyethylene terephthalate, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyether sulfone, poly ether ether ketone, polyallyl sulfone, thermoplastic polyimide, thermoplastic urethane resin, polyamino-bismaleimide, polyamide-imide, polyether-imide, bismaleimide-triazine resin, polymethylpentene, fluorine resin, liquid crystal polymer, olefin-vinyl alcohol copolymer, ionomer, polyarylate, acrylonitrile-ethylene-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, and acrylonitrile-styrene copolymer.

These resin components can be used alone or in combination of two or more.

Of the resin component, preferably, the epoxy resin is used.

The epoxy resin is in a state of liquid, semi-solid, or solid under normal temperature.

To be specific, examples of the epoxy resin include aromatic epoxy resins such as bisphenol epoxy resin (e.g., bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, hydrogenated bisphenol A epoxy resin, dimer acid-modified bisphenol epoxy resin, and the like), novolak epoxy resin (e.g., phenol novolak epoxy resin, cresol novolak epoxy resin, biphenyl epoxy resin, and the like), naphthalene epoxy resin, fluorene epoxy resin (e.g., bisaryl fluorene epoxy resin and the like), and triphenylmethane epoxy resin (e.g., trishydroxyphenylmethane epoxy resin and the like); nitrogen-containing-cyclic epoxy resins such as triepoxypropyl isocyanurate (triglycidyl isocyanurate) and hydantoin epoxy resin; aliphatic epoxy resin; alicyclic epoxy resin (e.g., dicyclo ring-type epoxy resin and the like); glycidylether epoxy resin; and glycidylamine epoxy resin.

These epoxy resins can be used alone or in combination of two or more.

Preferably, a combination of a liquid epoxy resin and a solid epoxy resin is used, or more preferably, a combination of a liquid aromatic epoxy resin and a solid aromatic epoxy resin is used. Examples of such a combination include, to be more specific, a combination of a liquid bisphenol epoxy resin and a solid triphenylmethane epoxy resin, and a combination of a liquid bisphenol epoxy resin and a solid bisphenol epoxy resin.

Preferably, a semi-solid epoxy resin is used alone, or more preferably, a semi-solid aromatic epoxy resin is used alone. Examples of those epoxy resins include, in particular, a semi-solid fluorene epoxy resin.

A combination of a liquid epoxy resin and a solid epoxy resin, or a semi-solid epoxy resin can improve conformability to irregularities (described later) of the thermal conductive layer 6.

The epoxy resin has an epoxy equivalent of, for example, 100 to 1000 g/eqiv., or preferably 160 to 700 g/eqiv., and has a softening temperature (ring and ball test) of, for example, 80° C. or less (to be specific, 20 to 80° C.), or preferably 70° C. or less (to be specific, 25 to 70° C.).

The epoxy resin has a melt viscosity at 80° C. of, for example, 10 to 20,000 mPa·s, or preferably 50 to 15,000 mPa·s. When two or more epoxy resins are used in combination, the melt viscosity of the mixture of these epoxy resins is set within the above-described range.

Furthermore, when an epoxy resin that is solid under normal temperature and an epoxy resin that is liquid under normal temperature are used in combination, a first epoxy resin having a softening temperature of, for example, below 45° C., or preferably 35° C. or less, and a second epoxy resin having a softening temperature of, for example, 45° C. or more, or preferably 55° C. or more are used in combination. In this way, the kinetic viscosity (in conformity with JIS K 7233, described later) of the resin component (mixture) can be set to a desired range, and also, conformability to irregularities of the thermal conductive layer 6 can be improved.

The epoxy resin can also be prepared as an epoxy resin composition containing, for example, an epoxy resin, a curing agent, and a curing accelerator.

The curing agent is a latent curing agent (epoxy resin curing agent) that allows the epoxy resin to cure by heating, and examples thereof include an imidazole compound, an amine compound, an acid anhydride compound, an amide compound, a hydrazide compound, and an imidazoline compound. In addition to the above-described compounds, a phenol compound, a urea compound, and a polysulfide compound can also be used.

Examples of the imidazole compound include 2-phenyl imidazole, 2-methyl imidazole, 2-ethyl-4-methyl imidazole, and 2-phenyl-4-methyl-5-hydroxymethyl imidazole.

Examples of the amine compound include aliphatic polyamines such as ethylene diamine, propylene diamine, and diethylene triamine, triethylene tetramine; and aromatic polyamines such as metha phenylenediamine, diaminodiphenyl methane, and diaminodiphenyl sulfone.

Examples of the acid anhydride compound include phthalic anhydride, maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methyl-hexahydrophthalic anhydride, methyl nadic anhydride, pyromelletic anhydride, dodecenylsuccinic anhydride, dichloro succinic anhydride, benzophenone tetracarboxylic anhydride, and chlorendic anhydride.

Examples of the amide compound include dicyandiamide and polyamide.

An example of the hydrazide compound includes adipic acid dihydrazide.

Examples of the imidazoline compound include methylimidazoline, 2-ethyl-4-methylimidazoline, ethylimidazoline, isopropylimidazoline, 2,4-dimethylimidazoline, phenylimidazoline, undecylimidazoline, heptadecylimidazoline, and 2-phenyl-4-methylimidazoline.

These curing agents can be used alone or in combination of two or more.

A preferable example of the curing agent is an imidazole compound.

Examples of the curing accelerator include tertiary amine compounds such as triethylenediamine and tri-2,4,6-dimethylaminomethylphenol; phosphorus compounds such as triphenylphosphine, tetraphenylphosphonium tetraphenylborate, and tetra-n-butylphosphonium-o,o-diethylphosphorodithioate; a quaternary ammonium salt compound; an organic metal salt compound; and derivatives thereof. These curing accelerators can be used alone or in combination of two or more.

In the epoxy resin composition, the mixing ratio of the curing agent is, for example, 0.5 to 50 parts by mass, or preferably 1 to 10 parts by mass per 100 parts by mass of the epoxy resin, and the mixing ratio of the curing accelerator is, for example, 0.1 to 10 parts by mass, or preferably 0.2 to 5 parts by mass per 100 parts by mass of the epoxy resin.

The above-described curing agent, and/or the curing accelerator can be prepared and used, as necessary, as a solution, i.e., the curing agent and/or the curing accelerator dissolved in a solvent; and/or as a dispersion liquid, i.e., the curing agent and/or the curing accelerator dispersed in a solvent.

Examples of the solvent include organic solvents including ketones such as acetone and methyl ethyl ketone (MEK), ester such as ethyl acetate, and amide such as N,N-dimethylformamide. Examples of the solvent also include aqueous solvents including water, and alcohols such as methanol, ethanol, propanol, and isopropanol. A preferable example is an organic solvent, more preferable examples are ketones and amides.

The resin component has a kinetic viscosity as measured in conformity with the kinetic viscosity test of JIS K 7233 (bubble viscometer method) (temperature: 25° C.±0.5° C., solvent: butyl carbitol, resin component (solid content) concentration: 40 mass %) of, for example, 0.22×10⁻⁴ to 2.00×10⁻⁴ m²/s, preferably 0.3×10⁻⁴ to 1.9×10⁻⁴ m²/s, or more preferably 0.4×10⁻⁴ to 1.8×10⁻⁴ m²/s. The above-described kinetic viscosity can also be set to, for example, 0.22×10⁻⁴ to 1.00×10⁻⁴ m²/s, preferably 0.3×10⁻⁴ to 0.9×10⁻⁴ m²/s, or more preferably 0.4×10⁻⁴ to 0.8×10⁻⁴ m²/s.

When the kinetic viscosity of the resin component exceeds the above-described range, excellent flexibility and conformability to irregularities (described later) may not be given to the thermal conductive layer 6. On the other hand, when the kinetic viscosity of the resin component is below the above-described range, boron nitride particles may not be oriented in a predetermined direction.

In the kinetic viscosity test in conformity with JIS K 7233 (bubble viscometer method), the kinetic viscosity of the resin component is measured by comparing the bubble rising speed of a resin component sample with the bubble rising speed of criterion samples (having a known kinetic viscosity), and determining the kinetic viscosity of the criterion sample having a matching rising speed to be the kinetic viscosity of the resin component.

In the thermal conductive layer 6, the proportion of the volume-based boron nitride particle content (solid content, that is, the volume percentage of boron nitride particles relative to a total volume of the resin component and the boron nitride particles) is, for example, 35 vol % or more, preferably 60 vol % or more, or more preferably 65 vol % or more, and usually, for example, 95 vol % or less, or preferably 90 vol % or less.

When the proportion of the volume-based boron nitride particle content is below the above-described range, the boron nitride particles may not be oriented in a predetermined direction in the thermal conductive layer 6. On the other hand, when the proportion of the volume-based boron nitride particle content exceeds the above-described range, the thermal conductive layer 6 may become fragile, and handleability may be reduced.

The mixing ratio by mass of the boron nitride particles relative to 100 parts by mass of the total amount of the components (boron nitride particles and resin component)(total solid content) forming the thermal conductive layer 6 is, for example, 40 to 95 parts by mass, or preferably 65 to 90 parts by mass, and the mixing ratio by mass of the resin component relative to 100 parts by mass of the total amount of the components forming the thermal conductive layer 6 is, for example, 5 to 60 parts by mass, or preferably 10 to 35 parts by mass. The mass-based mixing ratio of the boron nitride particles relative to 100 parts by mass of the resin component is, for example, 60 to 1900 parts by mass, or preferably 185 to 900 parts by mass.

When two epoxy resins (a first epoxy resin and a second epoxy resin) are used in combination, the mass ratio (mass of the first epoxy resin/mass of the second epoxy resin) of the first epoxy resin relative to the second epoxy resin can be set appropriately in accordance with the softening temperature and the like of the epoxy resins (the first epoxy resin and the second epoxy resin). For example, the mass ratio of the first epoxy resin relative to the second epoxy resin is 1/99 to 99/1, or preferably 10/90 to 90/10.

In the resin component, in addition to the above-described components (polymer), for example, a polymer precursor (e.g., a low molecular weight polymer including oligomer), and/or a monomer are contained.

Next, a method for forming the thermal conductive layer 6 is described.

In this method, first, the above-described components are blended at the above-described mixing ratio and are stirred and mixed, thereby preparing a mixture.

In the stirring and mixing, in order to mix the components efficiently, for example, the solvent can be blended therein with the above-described components, or, for example, the resin component (preferably, the thermoplastic resin component) can be melted by heating.

Examples of the solvent include the above-described organic solvents. When the above-described curing agent and/or the curing accelerator are prepared as a solvent solution and/or a solvent dispersion liquid, the solvent of the solvent solution and/or the solvent dispersion liquid can also serve as a mixing solvent for the stirring and mixing without adding a solvent during the stirring and mixing. Alternatively, in the stirring and mixing, a solvent can be further added as a mixing solvent.

In the case when the stirring and mixing is performed using a solvent, the solvent is removed after the stirring and mixing.

To remove the solvent, for example, the mixture is allowed to stand at room temperature for 1 to 48 hours; heated at 40 to 100° C. for 0.5 to 3 hours; or heated under a reduced pressure atmosphere of, for example, 0.001 to 50 kPa, at 20 to 60° C., for 0.5 to 3 hours.

When the resin component is to be melted by heating, the heating temperature is, for example, a temperature in the neighborhood of or exceeding the softening temperature of the resin component, to be specific, 40 to 150° C., or preferably 70 to 140° C.

Next, in this method, the obtained mixture is hot-pressed.

To be specific, as shown in FIG. 2( a), as necessary, for example, the mixture is hot-pressed with two releasing films 12 sandwiching the mixture, thereby producing a pressed sheet 6A. Conditions for the hot-pressing are as follows: a temperature of, for example, 50 to 150° C., or preferably 60 to 140° C.; a pressure of, for example, 1 to 100 MPa, or preferably 5 to 50 MPa; and a duration of, for example, 0.1 to 100 minutes, or preferably 1 to 30 minutes.

More preferably, the mixture is hot-pressed under vacuum. The degree of vacuum in the vacuum hot-pressing is, for example, 1 to 100 Pa, or preferably 5 to 50 Pa, and the temperature, the pressure, and the duration are the same as those described above for the hot-pressing.

When the temperature, the pressure, and/or the duration in the hot-pressing is outside the above-described range, there is a case where a porosity P (described later) of the thermal conductive layer 6 cannot be adjusted to give a desired value.

The pressed sheet 6A obtained by the hot-pressing has a thickness of, for example, 50 to 1000 μm, or preferably 100 to 800 μm.

Next, in this method, as shown in FIG. 2( b), the pressed sheet 6A is divided into a plurality of pieces (e.g., four pieces), thereby producing a divided sheet 6B (dividing step). In the division of the pressed sheet 6A, the pressed sheet 6A is cut along the thickness direction so that the pressed sheet 6A is divided into a plurality of pieces when the pressed sheet 6A is projected in the thickness direction. The pressed sheet 6A is cut so that the respective divided sheets 6B have the same shape when the divided sheets 6B are projected in the thickness direction.

Next, in this method, as shown in FIG. 2( c), the respective divided sheets 6B are laminated in the thickness direction, thereby producing a laminated sheet 6C (laminating step).

Thereafter, in this method, as shown in FIG. 2( a), the laminated sheet 6C is hot-pressed (preferably hot-pressed under vacuum) (hot-pressing step). The conditions for the hot-pressing are the same as the above-described conditions for the hot-pressing of mixture.

The thickness of the hot-pressed laminated sheet 6C is, for example, 1 mm or less, or preferably 0.8 mm or less, and usually is, for example, 0.05 mm or more, or preferably 0.1 mm or more.

Thereafter, as shown in FIG. 3, the series of the steps of the above-described dividing step (FIG. 2( b)), laminating step (FIG. 2( c)), and hot-pressing step (FIG. 2( a)) are performed repeatedly, so as to allow boron nitride particles 8 to be efficiently oriented in a predetermined direction in the resin component 9 in the thermal conductive layer 6. The number of the repetition is not particularly limited, and can be set appropriately according to the charging state of the boron nitride particles. The number of the repetition is, for example, 1 to 10 times, or preferably 2 to 7 times.

In the above-described hot-pressing step (FIG. 2( a)), for example, a plurality of calendering rolls and the like can also be used for rolling the mixture and the laminated sheet 6C.

The thermal conductive layer 6 shown in FIG. 3 and FIG. 4 can be formed in this manner.

The thermal conductive layer 6 thus formed has a thickness of, for example, 1 mm or less, or preferably 0.8 mm or less, and, for example, 0.05 mm or more, or preferably 0.1 mm or more.

In the thermal conductive layer 6, the proportion of the volume-based boron nitride particle 8 content (solid content, that is, volume percentage of boron nitride particles 8 relative to the total volume of the resin component 9 and the boron nitride particles 8) is, as described above, for example, 35 vol % or more (preferably 60 vol % or more, or more preferably 75 vol % or more), and usually 95 vol % or less (preferably 90 vol % or less).

When the proportion of the boron nitride particle 8 content is below the above-described range, the boron nitride particles 8 may not be oriented in a predetermined direction in the thermal conductive layer 6.

When the resin component 9 is the thermosetting resin component, for example, the series of the steps of the above-described dividing step (FIG. 2( b)), laminating step (FIG. 2( c)), and hot-pressing step (FIG. 2( a)) are performed repeatedly for an uncured thermal conductive layer 6, thereby producing an uncured thermal conductive layer 6 as is. The uncured thermal conductive layer 6 is cured by heating when the thermal conductive adhesive sheet 5 is allowed to adhere to the electronic components 3 and the substrate 2.

In the thus formed thermal conductive layer 6, as shown in FIG. 3 and its partially enlarged schematic view, the longitudinal direction LD of the boron nitride particle 8 is oriented along a plane (surface) direction SD that crosses (is perpendicular to) the thickness direction TD of the thermal conductive layer 6.

The calculated average of the angle formed between the longitudinal direction LD of the boron nitride particle 8 and a plane direction SD of the thermal conductive layer 6 (orientation angle a of the boron nitride particles 8 relative to the thermal conductive layer 6) is, for example, 25 degrees or less, or preferably 20 degrees or less, and usually 0 degree or more.

The orientation angle a of the boron nitride particle 8 relative to the thermal conductive layer 6 is obtained as follows: the thermal conductive layer 6 is cut along the thickness direction with a cross section polisher (CP); the cross section thus appeared is photographed with a scanning electron microscope (SEM) at a magnification that enables observation of 200 or more boron nitride particles 8 in the field of view; a tilt angle a between the longitudinal direction LD of the boron nitride particle 8 and the plane direction SD (direction perpendicular to the thickness direction TD) of the thermal conductive layer 6 is obtained from the obtained SEM photograph; and the average value of the tilt angles α is calculated.

Thus, the thermal conductivity in the plane direction SD of the thermal conductive layer 6 is 4 W/m·K or more, preferably 5 W/m·K or more, more preferably 10 W/m·K or more, even more preferably 15 W/m·K or more, or particularly preferably 25 W/m·K or more, and usually 200 W/m·K or less.

The thermal conductivity in the plane direction SD of the thermal conductive layer 6 is substantially the same before and after the curing by heat when the resin component 9 is the thermosetting resin component.

When the thermal conductivity in the plane direction SD of the thermal conductive layer 6 is below the above-described range, thermal conductivity in the plane direction SD is insufficient, and therefore there is a case where the thermal conductive layer 6 cannot be used for heat dissipation that requires thermal conductivity in such a plane direction SD.

The thermal conductivity in the plane direction SD of the thermal conductive layer 6 is measured by a pulse heating method. In the pulse heating method, the xenonflash analyzer “LFA-447” (manufactured by Erich NETZSCH GmbH & Co. Holding KG) is used.

The thermal conductivity in the thickness direction TD of the thermal conductive layer 6 is, for example, 0.5 to 15 W/m·K, or preferably 1 to 10 W/m·K.

The thermal conductivity in the thickness direction TD of the thermal conductive layer 6 is measured by a pulse heating method, a laser flash method, or a TWA method. In the pulse heating method, the above-described device is used, in the laser flash method, “TC-9000” (manufactured by Ulvac, Inc.) is used, and in the TWA method, “ai-Phase mobile” (manufactured by ai-Phase Co., Ltd) is used.

Thus, the ratio of the thermal conductivity in the plane direction SD of the thermal conductive layer 6 relative to the thermal conductivity in the thickness direction TD of the thermal conductive layer 6 (thermal conductivity in the plane direction SD/thermal conductivity in the thickness direction TD) is, for example, 1.5 or more, preferably 3 or more, or more preferably 4 or more, and usually 20 or less.

Although not shown in FIG. 3, for example, pores (gaps) are formed in the thermal conductive layer 6.

The proportion of the pores in the thermal conductive layer 6, that is, a porosity P, can be adjusted by setting the proportion of the boron nitride particle 8 content (volume-based), and further setting the temperature, the pressure, and/or the duration at the time of hot pressing the mixture of the boron nitride particle 8 and the resin component 9 (FIG. 2( a)). To be specific, the porosity P can be adjusted by setting the temperature, the pressure, and/or the duration of the hot pressing (FIG. 2( a)) within the above-described range.

The porosity P of the thermal conductive layer 6 is, for example, 30 vol % or less, or preferably 10 vol % or less.

The porosity P is measured by, for example, as follows: the thermal conductive layer 6 is cut along the thickness direction with a cross section polisher (CP); the cross section thus appeared is observed with a scanning electron microscope (SEM) at a magnification of 200 to obtain an image; the obtained image is binarized based on the pore portion and the non-pore portion; and the area ratio, i.e., the ratio of the pore portion area to the total area of the cross section of the thermal conductive layer 6, is determined by calculation.

The thermal conductive layer 6 has a porosity P2 after curing of, relative to a porosity P1 before curing, for example, 100% or less, in particular, or less, or preferably 50% or less.

For the measurement of the porosity P (P1), when the resin component 9 is a thermosetting resin component, the thermal conductive layer 6 before curing by heat is used.

When the porosity P of the thermal conductive layer 6 is within the above-described range, the conformability to irregularities (described later) of the thermal conductive layer 6 can be improved.

When the thermal conductive layer 6 is evaluated in the bend test in conformity with the cylindrical mandrel method of JIS K 5600-5-1 under the test conditions shown below, preferably, no fracture is observed.

Test Conditions:

Test Device: Type I

Mandrel: diameter 10 mm

Bending Angle: 90 degrees or more

Thickness of the thermal conductive layer 6: 0.3 mm

FIGS. 10 and 11 show perspective views of the Type I test device. In the following, the Type I test device is described.

In FIGS. 10 and 11, a Type I test device 90 includes a first flat plate 91; a second flat plate 92 disposed in parallel with the first flat plate 91; and a mandrel (rotation axis) 93 provided for allowing the first flat plate 91 and the second flat plate 92 to rotate relatively.

The first flat plate 91 is formed into a generally rectangular flat plate. A stopper 94 is provided at one end portion (free end portion) of the first flat plate 91. The stopper 94 is formed on the surface of the second flat plate 92 so as to extend along the one end portion of the second flat plate 92.

The second flat plate 92 is formed into a generally rectangular flat plate, and one side thereof is disposed so as to be adjacent to one side (the other end portion (proximal end portion) that is opposite to the one end portion where the stopper 94 is provided) of the first flat plate 91.

The mandrel 93 is formed so as to extend along one side of the first flat plate 91 and one side of the second flat plate 92 that are adjacent to each other.

In the Type I test device 90, as shown in FIG. 10, the surface of the first flat plate 91 is flush with the surface of the second flat plate 92 before the start of the bend test.

To perform the bend test, the thermal conductive layer 6 is placed on the surface of the first flat plate 91 and the surface of the second flat plate 92. The thermal conductive layer 6 is placed so that one side of the thermal conductive layer 6 is in contact with the stopper 94.

Then, as shown in FIG. 11, the first flat plate 91 and the second flat plate 92 are rotated relatively. In particular, the free end portion of the first flat plate 91 and the free end portion of the second flat plate 92 are rotated to a predetermined angle with the mandrel 93 as the center. To be specific, the first flat plate 91 and the second flat plate 92 are rotated so as to bring the surface of the free end portions thereof closer (oppose each other).

In this way, the thermal conductive layer 6 is bent with the mandrel 93 as the center, conforming to the rotation of the first flat plate 91 and the second flat plate 92.

More preferably, no fracture is observed in the thermal conductive layer 6 even when the bending angle is set to 180 degrees under the above-described test conditions.

When the resin component 9 is the thermosetting resin component, a semi-cured (in B-stage) thermal conductive layer 6 is tested in the bend test.

When the fracture is observed in the bend test with the above-described bending angle in the thermal conductive layer 6, there is a case where excellent flexibility cannot be given to the thermal conductive layer 6.

Furthermore, for example, when the thermal conductive layer 6 is evaluated in the 3-point bending test in conformity with JIS K 7171 (2008) under the test conditions shown below, no fracture is observed.

Test Conditions:

Test piece: size 20 mm×15 mm

Distance between supporting points: 5 mm

Testing speed: 20 mm/min (indenter depressing speed)

Bending angle: 120 degrees

Evaluation method: presence or absence of fracture such as cracks at the center of the test piece is observed visually when tested under the above-described test conditions.

In the 3-point bending test, when the resin component 3 is a thermosetting resin component, the thermal conductive layer 6 before curing by heat is used.

Therefore, the thermal conductive layer 6 is excellent in conformability to irregularities because no fracture is observed in the above-described 3-point bending test. The conformability to irregularities is, when the thermal conductive layer 6 is provided on an object (e.g., the above-described substrate 2 and the like) with irregularities, a property of the thermal conductive layer 6 that conforms to be in close contact with the irregularities (e.g., the above-described irregularities formed by the electronic component 3).

A mark such as, for example, letters and symbols can be adhered to the thermal conductive layer 6. That is, the thermal conductive layer 6 is excellent in mark adhesion. The mark adhesion is a property of the thermal conductive layer 6 that allows reliable adhesion of the above-described mark thereon.

The mark can be adhered (applied, fixed, or firmly fixed) to the thermal conductive layer 6, to be specific, by printing, engraving, or the like.

Examples of printing include, for example, inkjet printing, relief printing, intaglio printing, and laser printing.

When the mark is to be printed by inkjet printing, relief printing, or intaglio printing, for example, an ink fixing layer for improving mark's fixed state can be provided on the surface (printing side, top face, or the other side relative to the adhesive/pressure-sensitive adhesive layer 7) of the thermal conductive layer 6.

When the mark is to be printed by laser printing, for example, a toner fixing layer for improving mark's fixed state can be provided on the surface (printing side, top face, or the other side relative to the adhesive/pressure-sensitive adhesive layer 7) of the thermal conductive layer 6.

Examples of engraving include laser engraving, and punching.

The thermal conductive layer 6 is insulative, and has pressure-sensitive adhesiveness (slightly tacky).

To be specific, the thermal conductive layer 6 has a volume resistivity (JIS K6271) of, for example, 1×10¹⁰ Ω·cm or more, preferably 1×10¹² Ω·cm or more, and usually 1×10²⁰ Ω·cm or less.

The volume resistivity R of the thermal conductive layer 6 is measured in conformity with JIS K 6911 (thermosetting plastic general testing method, 2006).

When the thermal conductive layer 6 has a volume resistivity R below the above-described range, there is a case where short circuits between the electron devices to be described later cannot be prevented.

When the resin component 9 is a thermosetting resin component in the thermal conductive layer 6, the volume resistivity R is a value of a cured thermal conductive layer 6.

The thermal conductive layer 6 does not fall off from, for example, an adherend in the initial adhesion test (1) described below. That is, a temporary fixed state between the thermal conductive layer 6 and the adherend is kept.

Initial Adhesion Test (1): The thermal conductive layer 6 is thermocompression bonded on top of an adherend that is placed along a horizontal direction to be temporary fixed thereon, and then allowed to stand for 10 minutes, and thereafter, the adherend is turned over to be upside down.

Examples of the adherend include the above-described substrate 2 on which electronic components are mounted. In pressure bonding, for example, while a sponge roll made of a resin such as silicone resin is pressed against the thermal conductive layer 6, the sponge roll is rolled on the surface of the thermal conductive layer 6.

The temperature of the thermocompression bonding is, when the resin component 9 is a thermosetting resin component (e.g., epoxy resin), for example, 80° C.

On the other hand, when the resin component 9 is a thermoplastic resin component (e.g., polyethylene), the temperature of the thermocompression bonding is a temperature higher by 10 to 30° C. than the softening point or the melting point of the thermoplastic resin component; preferably a temperature higher by 15 to 25° C. than the softening point or the melting point of the thermoplastic resin component; more preferably, a temperature higher by 20° C. than the softening point or the melting point of the thermoplastic resin component; or to be specific, a temperature of 120° C. (that is, the softening point or the melting point of the thermoplastic resin component is 100° C., and the temperature higher by 20° C. than 100° C. is 120° C.).

When the thermal conductive layer 6 falls off from the adherend in the above-described initial adhesion test (1), that is, when the temporary fixed state between the thermal conductive layer 6 and the adherend is not kept, there is a case where the thermal conductive layer 6 cannot be reliably temporary fixed to the adherend.

When the resin component 9 is a thermosetting resin component, the thermal conductive layer 6 to be tested in the initial adhesion test (1) and the initial adhesion test (2) (described later) is a thermal conductive layer 6 before curing, and the thermal conductive layer 6 will be in B-stage based on the thermocompression bonding in the initial adhesion test (1) and the initial adhesion test (2).

When the resin component 9 is a thermoplastic resin component, the thermal conductive layer 6 to be tested in the initial adhesion test (1) and the initial adhesion test (2) (described later) is a solid thermal conductive layer 6, and the thermal conductive layer 6 is softened by the thermocompression bonding in the initial adhesion test (1) and the initial adhesion test (2).

Preferably, the thermal conductive layer 6 does not fall off from the adherend in both of the above-described initial adhesion test (1) and the initial adhesion test (2) described below. That is, a temporary fixed state between the thermal conductive layer 6 and the adherend is kept.

Initial Adhesion Test (2): The thermal conductive layer 6 is thermocompression bonded on top of an adherend that is placed along a horizontal direction to be temporary fixed thereon, and then allowed to stand for 10 minutes, and thereafter, the adherend is disposed along a vertical direction (up-down directions).

The temperature in the thermocompression bonding of the Initial Adhesion Test (2) is the same as the temperature of thermocompression bonding in the Initial Adhesion Test (1).

The adhesive/pressure-sensitive adhesive layer 7 is formed, as shown in FIG. 4, on the back face of the thermal conductive layer 6. To be specific, the adhesive/pressure-sensitive adhesive layer 7 is formed, as shown in FIG. 1, on the bottom face of the thermal conductive layer 6 that is facing the substrate 2 exposed from the electronic components 3.

The adhesive/pressure-sensitive adhesive layer 7 is composed of an adhesive having flexibility and adhesiveness or pressure-sensitive adhesiveness (tackiness) under a normal temperature atmosphere and a heated atmosphere, and is capable of exhibiting adhesive effects by heating or by cooling after the heating; or a pressure-sensitive adhesive having flexibility and adhesiveness or pressure-sensitive adhesiveness (tackiness) under a normal temperature atmosphere and a heated atmosphere, and is capable of exhibiting pressure-sensitive adhesive effects (effects of pressure-sensitive adhesion, that is, pressure-sensitive adhesion effects) by heating or cooling after the heating.

Examples of the adhesive include a thermosetting adhesive and a hot-melt adhesive.

The thermosetting adhesive adheres to the substrate 2 by being cured by heating and solidified. Examples of the thermosetting adhesive include an epoxy thermosetting adhesive, a urethane thermosetting adhesive, and an acrylic thermosetting adhesive. Preferably, an epoxy thermosetting adhesive is used.

The curing temperature of the thermosetting adhesive is, for example, 100 to 200° C.

The hot-melt adhesive is melted or softened by heating, heat-fused to the substrate 2, and adhered to the substrate 2 by cooling afterward to be solidified. Examples of the hot-melt adhesive include a rubber hot-melt adhesive, a polyester hot-melt adhesive, and an olefin hot-melt adhesive. Preferably, a rubber hot-melt adhesive is used.

The hot-melt adhesive has a softening temperature (ring and ball method) of, for example, 100 to 200° C. The hot-melt adhesive has a melt viscosity at 180° C. of, for example, 100 to 30,000 mPa·s.

The above-described adhesive can also contain, as necessary, for example, thermal conductive particles.

Examples of the thermal conductive particles include thermal conductive inorganic particles and thermal conductive organic particles. Preferably, thermal conductive inorganic particles are used.

Examples of the thermal conductive inorganic particles include nitride particles such as boron nitride particles, aluminum nitride particles, silicon nitride particles, gallium nitride particles; hydroxide particles such as aluminum hydroxide particles and magnesium hydroxide particles; oxide particles such as silicon oxide particles, aluminum oxide particles, titanium oxide particles, zinc oxide particles, tin oxide particles, copper oxide particles, and nickel oxide particles; carbide particles such as silicon carbide particles; carbonate particles such as calcium carbonate particles; metallate (metal salts of acids) particles such as titanate particles including barium titanate particles and potassium titanate particles; and metal particles such as copper particles, silver particles, gold particles, nickel particles, aluminum particles, and platinum particles.

These thermal conductive particles can be used alone or in combination of two or more.

Examples of the shape or form of the thermal conductive particle include a bulk form, a needle shape, a plate shape, a layered form, and a tube shape. The thermal conductive particles have an average particle size (maximum length) of, for example, 0.1 to 1000 μm.

The thermal conductive particles have, for example, anisotropic thermal conductivity or isotropic thermal conductivity. Preferably, the thermal conductive particles have isotropic thermal conductivity.

The thermal conductive particles have a thermal conductivity of, for example, 1 W/m·K or more, preferably 2 W/m·K or more, or more preferably 3 W/m·K or more, and usually 1000 W/m·K or less.

The mixing ratio of the thermal conductive particles is, for example, 190 parts by mass or less, or preferably 900 parts by mass or less per 100 parts by mass of the resin component in the adhesive. The volume-based mixing ratio of the thermal conductive particles is 95 vol % or less, or preferably 90 vol % or less.

When the thermal conductive particles are to be blended into the adhesive, the thermal conductive particles are added to the adhesive at the above-described mixing ratio, and the mixture is stirred to be mixed.

The adhesive is thus prepared as a thermal conductive adhesive.

The thermal conductive adhesive has a thermal conductivity of, for example, 0.01 W/m·K or more, and usually has a thermal conductivity of 100 W/m·K or less.

Examples of the pressure-sensitive adhesive include known pressure-sensitive adhesives, and the pressure-sensitive adhesive is selected appropriately from those known pressure-sensitive adhesives such as, for example, an acrylic pressure-sensitive adhesive, a silicone pressure-sensitive adhesive, a rubber pressure-sensitive adhesive, a vinylalkylether pressure-sensitive adhesive, a polyester pressure-sensitive adhesive, a polyamide pressure-sensitive adhesive, a urethane pressure-sensitive adhesive, and a styrene-diene block copolymer pressure-sensitive adhesive. The pressure-sensitive adhesive can be used alone or in combination of two or more. Preferable examples of the pressure-sensitive adhesive include an acrylic pressure-sensitive adhesive, a silicone pressure-sensitive adhesive, and a rubber pressure-sensitive adhesive, and more preferable examples are an acrylic pressure-sensitive adhesive and a silicone pressure-sensitive adhesive. The pressure-sensitive adhesive can be prepared as a thermal conductive pressure-sensitive adhesive by adding the above-described thermal conductive particles to the pressure-sensitive adhesive at the above-described ratio. The thermal conductivity of the thermal conductive pressure-sensitive adhesive is the same as that of the above-described thermal conductivity of the thermal conductive adhesive.

The adhesive/pressure-sensitive adhesive layer 7 has a thickness T of, for example, 50 μm or less, preferably 25 μm or less, or more preferably 15 μm or less, and usually, the thickness T is 1 μm or more. When the thickness T of the adhesive/pressure-sensitive adhesive layer 7 exceeds the above-described range, there is a case where the heat generated from the electronic components 3 may not be conducted from the thermal conductive layer 6 to the frame 4 through the adhesive/pressure-sensitive adhesive layer 7.

To obtain the thermal conductive adhesive sheet 5, as shown in FIG. 4, first, the above-described thermal conductive layer 6 is prepared, and then the adhesive/pressure-sensitive adhesive layer 7 is laminated onto the back face of the thermal conductive layer 6.

To be specific, a varnish is prepared by blending the above-described solvent with an adhesive (preferably, thermosetting adhesive) or a pressure-sensitive adhesive and dissolving the adhesive or pressure-sensitive adhesive, and the varnish is applied on the surface of a separator, and thereafter, the organic solvent in the varnish is distilled away by drying under normal pressure or vacuum (reduced pressure). The varnish has a solid content concentration of, for example, 10 to 90 mass %.

Thereafter, the adhesive/pressure-sensitive adhesive layer 7 is bonded to the thermal conductive layer 6. When the adhesive/pressure-sensitive adhesive layer 7 and the thermal conductive layer 6 are bonded, as necessary, they are pressure bonded or thermocompression bonded.

Next, a method for producing the heat dissipation structure 1 is described with reference to FIG. 5.

First, in this method, as shown in FIG. 5, the substrate 2 on which the electronic components 3 are mounted is fixed to the housing (not shown) which supports the frame 4, and the thermal conductive adhesive sheet 5 is prepared.

The thermal conductive adhesive sheet 5 is trimmed so as to include the substrate 2 when the thermal conductive adhesive sheet 5 is projected in the thickness direction. To be specific, the thermal conductive adhesive sheet 5 is cut and processed to such a size that a center portion and one end portion thereof overlap with the substrate 2, and the other end portion thereof does not overlap with the substrate 2.

Next, in this method, as shown in FIG. 5, the thermal conductive adhesive sheet 5 is thermocompression bonded to the electronic components 3 and substrate 2, and to the frame 4.

To be specific, the center portion and one end portion of the thermal conductive adhesive sheet 5 are thermocompression bonded to the electronic components 3 and the substrate 2, and the other end portion of the thermal conductive adhesive sheet 5 is thermocompression bonded to the frame 4.

In detail, first, as shown by the phantom line in FIG. 5, the thermal conductive adhesive sheet 5 and the substrate 2 are disposed so that the center portion and one end portion of the adhesive/pressure-sensitive adhesive layer 7 face the electronic components 3; and the other end portion of the thermal conductive adhesive sheet 5 is bent.

Then, as indicated by the arrows in FIG. 5, the center portion and one end portion of the thermal conductive adhesive sheet 5 are brought into contact with the electronic components 3 and the substrate 2, and the other end portion of the thermal conductive adhesive sheet 5 is brought into contact with the frame 4. Then, while the thermal conductive adhesive sheet 5 is being heated, the center portion and one end portion of the thermal conductive adhesive sheet 5 are pressure bonded (pressed, that is, thermocompression bonded) to the substrate 2, and the other end portion of the thermal conductive adhesive sheet 5 is pressure bonded (pressed, that is, thermocompression bonded) to the frame 4.

In the pressure bonding, for example, while a sponge roll made of a resin such as silicone resin is pressed against the thermal conductive adhesive sheet 5, the sponge roll is rolled on the surface of the thermal conductive adhesive sheet 5 (top face of the thermal conductive layer 6).

The heating temperature is, for example, 40 to 120° C.

In this thermocompression bonding, flexibility of the adhesive/pressure-sensitive adhesive layer 7 improves, and therefore, as can be seen in FIG. 1, the electronic components 3 that project from the surface (top face) to a front side (upper side) of the substrate 2 penetrate (break) through the adhesive/pressure-sensitive adhesive layer 7, and the surface (top face) of the electronic components 3 is brought into contact with the back face (bottom face) of the thermal conductive layer 6. The gap (e.g., the gap between the resistor 23 and the substrate 2) 14 formed around the electronic components 3 is filled with the adhesive/pressure-sensitive adhesive layer 7. Furthermore, the adhesive/pressure-sensitive adhesive layer 7 is entangled with and covers a terminal which is not shown, and/or a wire 15, for connecting the electronic components 3 (to be specific, IC chips 20 and resistor 23) and the substrate 2.

To be specific, the top face and an upper portion of the side face of the electronic components 3 are covered with the thermal conductive layer 6.

On the other hand, a lower portion of the side face of the electronic components 3 is covered (adhered to or pressure-sensitively adhered to) with the adhesive/pressure-sensitive adhesive layer 7 that is penetrated (broken) by the electronic components 3.

To be more specific, in thermocompression bonding, when the resin component 9 is a thermosetting resin component, the resin component 9 is in B-stage, and therefore the thermal conductive layer 6 is pressure-sensitively adhered to the surface (top face) of the substrate 2 exposed from the electronic components 3. Furthermore, when the electronic components 3 have a thickness that is larger than that of the adhesive/pressure-sensitive adhesive layer 7, the upper portion of the electronic components 3 enters into the thermal conductive layer 6 toward the inner portion from the back face of the thermal conductive layer 6.

When the adhesive is a hot-melt adhesive, the above-described thermocompression bonding allows the adhesive/pressure-sensitive adhesive layer 7 to be melted or softened, allowing the center portion and one end portion of the adhesive/pressure-sensitive adhesive layer 7 to be heat-fused on the surface of the substrate 2 and the side face of the electronic components 3, and also allowing the other end portion of the adhesive/pressure-sensitive adhesive layer 7 to be heat-fused on the inner face of the frame 4.

When the adhesive is a thermosetting adhesive, the above-described thermocompression bonding allows the adhesive/pressure-sensitive adhesive layer 7 to be in B-stage, allowing the center portion and one end portion of the adhesive/pressure-sensitive adhesive layer 7 to be temporary fixed to the top face of the substrate 2 and side face of the electronic components 3, and allowing the other end portion of the adhesive/pressure-sensitive adhesive layer 7 to be temporary fixed to the inner face of the frame 4.

Thereafter, when the resin component 9 is a thermosetting resin component, the thermal conductive layer 6 is allowed to be cured by heating, and when the adhesive is a thermosetting adhesive, the adhesive/pressure-sensitive adhesive layer 7 is allowed to be cured by heating.

To cure the thermal conductive layer 6 and the adhesive/pressure-sensitive adhesive layer 7 by heating, for example, the frame 4, substrate 2, and electronic components 3 to which the thermal conductive adhesive sheet 5 is temporary fixed are introduced into a dryer. The conditions for the thermosetting are, for example, a heating temperature of 100 to 250° C., or preferably 120 to 200° C., and a heating time of, for example, 10 to 200 minutes, or preferably 60 to 150 minutes.

The center portion and one end portion of the thermal conductive adhesive sheet 5 are thus adhered to the electronic components 3 and the substrate 2, and the other end portion of the thermal conductive adhesive sheet 5 is adhered to the frame 4.

In the above-described heat dissipation structure 1, the electronic components 3 are covered with the thermal conductive adhesive sheet 5, and therefore the heat generated from the electronic components 3 can be conducted from the top face and side face of the electronic components 3 to the thermal conductive adhesive sheet 5. Then, the heat is conducted from the thermal conductive adhesive sheet 5 to the frame 4, and the heat can be dissipated to outside at the frame 4.

Therefore, the heat generated from the electronic components 3 can be dissipated efficiently by the thermal conductive adhesive sheet 5 and the frame 4.

Moreover, with easy and excellent workability, i.e., the thermal conductive adhesive sheet 5 is provided on the substrate 2 so as to cover the electronic components 3, the heat generated from the electronic components 3 can be dissipated.

FIG. 6 shows a cross-sectional view of another embodiment (embodiment in which the thermal conductive adhesive sheet is composed of a thermal conductive layer) of the heat dissipation structure of the present invention, FIG. 7 shows a process drawing for describing production of the heat dissipation structure of FIG. 6, FIG. 8 shows a cross-sectional view of another embodiment (embodiment in which the other end portion of the thermal conductive adhesive sheet is in contact with the housing) of the heat dissipation structure of the present invention, and FIG. 9 shows a cross-sectional view of another embodiment (embodiment in which the adhesive/pressure-sensitive adhesive layer is in contact with the top face of the electronic components) of the heat dissipation structure of the present invention.

In the following figures, the same reference numerals are used for the members that are the same as the members in the above, and detailed descriptions thereof are omitted.

Although the adhesive/pressure-sensitive adhesive layer 7 is provided in the thermal conductive adhesive sheet 5 in the description above, for example, as shown in FIG. 6, the thermal conductive adhesive sheet 5 can also be formed from the thermal conductive layer 6 without providing the adhesive/pressure-sensitive adhesive layer 7.

In FIG. 6, the side face of the electronic components 3 is in contact with the thermal conductive layer 6. To be specific, the top face of the substrate 2 exposed from the electronic components 3 and the entire side face of the electronic components 3 are in contact with the thermal conductive layer 6.

To obtain this heat dissipation structure 1, as shown in FIG. 7, the substrate 2 on which the electronic components 3 are mounted is fixed to the housing (not shown) that supports the frame 4, thereby preparing the thermal conductive adhesive sheet 5. The thermal conductive adhesive sheet 5 is composed of the thermal conductive layer 6.

Then, as shown by the phantom line in FIG. 7, the thermal conductive adhesive sheet 5 is bent, and then as indicated by the arrows in FIG. 7, the center portion and one end portion of the thermal conductive adhesive sheet 5 are thermocompression bonded to the electronic components 3 and the substrate 2, and the other end portion of the thermal conductive adhesive sheet 5 is thermocompression bonded to the frame 4.

In the thermocompression bonding of the thermal conductive adhesive sheet 5, when the resin component 9 is a thermosetting resin component, the resin component 9 is in B-stage, and therefore the gap 14 formed around the electronic components 3 is filled with the thermal conductive layer 6.

The thermal conductive adhesive sheet 5 is thus temporary fixed to the substrate 2 and the frame 4.

Thereafter, when the resin component 9 is a thermosetting resin component, the thermal conductive layer 6 is cured by heating.

The center portion and one end portion of the thermal conductive layer 6 are thus adhered to the top face and the side face of the electronic components 3, and to the top face of the substrate 2 exposed from the electronic components 3; and the other end portion of the thermal conductive layer 6 is adhered to the right side face of the frame 4.

In this heat dissipation structure 1, the thermal conductive layer 6 is directly in contact with the surface of the electronic components 3 and the right side face of the frame 4. Thus, in the heat dissipation structure 1 of FIG. 6, the heat generated from the electronic components 3 can be dissipated more efficiently through the thermal conductive layer 6 compared with the heat dissipation structure 1 of FIG. 1.

On the other hand, in the heat dissipation structure 1 of FIG. 1, because the thermal conductive layer 6 is adhered to the substrate 2 and the frame 4 by the adhesive/pressure-sensitive adhesive layer 7, the thermal conductive adhesive sheet 5 can be more reliably adhered thereto, and more excellent heat dissipation can be exhibited for a long period of time compared with the heat dissipation structure 1 of FIG. 6.

Although the frame 4 is given as an example of the heat dissipation member of the present invention in the description above with reference to FIG. 1 and FIG. 6, the heat dissipation member is not limited to the frame 4, and examples thereof also include a housing 10 (FIG. 8), a heat sink (not shown), and a reinforcement beam (not shown).

In FIG. 8, the housing 10 has a shape of a bottomed box having an opening at an upper side thereof, and integrally includes a bottom wall 13, and a side wall 11 extending upward from a peripheral end portion of the bottom wall 13. The side wall 11 is disposed around the substrate 2, and the bottom wall 13 is disposed below the substrate 2. The housing 10 is formed from, for example, metals such as aluminum, stainless steel, copper, and iron.

The thermal conductive adhesive sheet 5 is disposed such that a portion of the other end side from the center portion of the thermal conductive adhesive sheet 5 is bent downward from one end edge of the substrate 2, and the other end portion of the thermal conductive adhesive sheet 5 extends downward at the right side face (inner face) of the frame 4. The other end portion of the thermal conductive adhesive sheet 5 is in contact with a lower portion (to be specific, in the proximity of the connecting portion of the side wall 11 and the bottom wall 13) of the right side face of the frame 4.

Although the adhesive/pressure-sensitive adhesive layer 7 is laminated onto one side (back face) of the thermal conductive layer 6 in the description above, for example, as shown by the phantom line in FIG. 1 and the phantom line in FIG. 4, the adhesive/pressure-sensitive adhesive layer 7 can be formed on both sides (front face and back face) of the thermal conductive adhesive sheet 5.

Although the thermocompression bonding is performed so that the adhesive/pressure-sensitive adhesive layer 7 is penetrated by the electronic components 3 in the above description with reference to FIG. 1, for example, as shown in FIG. 9, the thermocompression bonding can be performed so that the adhesive/pressure-sensitive adhesive layer 7 covers the top face of the electronic components 3 without being penetrated by the electronic components 3.

The adhesive/pressure-sensitive adhesive layer 7 is in contact with the top face of the electronic components 3, but is not in contact with the top face of the substrate 2 exposed from the electronic components 3, and is disposed so that a space (gap) is provided between the adhesive/pressure-sensitive adhesive layer 7 and the top face of the substrate 2.

In this heat dissipation structure 1 as well, the heat from the electronic components 3 can be conducted to the thermal conductive layer 6 through the adhesive/pressure-sensitive adhesive layer 7, and furthermore, this thermal conductive layer 6 can transport the heat to the heat dissipation member 4.

EXAMPLES

Hereinafter, the present invention is described in further detail with reference to Preparation Examples, Examples, and Production Examples. However, the present invention is not limited to Examples.

(Preparation of Thermal Conductive Layer) Preparation Example 1

The components described below were blended, stirred, and allowed to stand at room temperature (23° C.) for one night, thereby allowing methyl ethyl ketone (dispersion medium for the curing agent) to volatilize and preparing a semi-solid mixture. The details of the components were as follows: 13.42 g of PT-110 (trade name, plate-like boron nitride particles, average particle size (light scattering method) 45 μm, manufactured by Momentive Performance Materials Inc.), 1.0 g of jER®828 (trade name, bisphenol A epoxy resin, first epoxy resin, liquid, epoxy equivalent 184 to 194 g/eqiv., softening temperature (ring and ball method) below 25° C., melt viscosity (80° C.) 70 mPa·s, manufactured by Japan Epoxy Resins Co., Ltd.), 2.0 g of EPPN-501HY (trade name, triphenylmethane epoxy resin, second epoxy resin, solid, epoxy equivalent 163 to 175 g/eqiv., softening temperature (ring and ball method) 57 to 63° C., manufactured by NIPPON KAYAKU Co., Ltd), and 3 g (solid content 0.15 g) (5 mass % per total amount of epoxy resins of jER®828 and EPPN-501HY) of a curing agent (a dispersion liquid of 5 mass % Curezol® 2P4MHZ-PW (trade name, manufactured by Shikoku Chemicals Corporation.) in methyl ethyl ketone).

In the above-described blending, the volume percentage (vol %) of the boron nitride particles relative to the total volume of the solid content excluding the curing agent (that is, solid content of the boron nitride particle and epoxy resin) was 70 vol %.

Then, the obtained mixture was sandwiched by two silicone-treated releasing films, and then these were hot-pressed with a vacuum hot-press at 80° C. under an atmosphere (vacuum atmosphere) of 10 Pa with a load of 5 tons (20 MPa) for 2 minutes. A pressed sheet having a thickness of 0.3 mm was thus obtained (ref: FIG. 2( a)).

Thereafter, the obtained pressed sheet was cut so as to be divided into a plurality of pieces when projected in the thickness direction of the pressed sheet. Divided sheets were thus obtained (ref: FIG. 2( b)). Next, the divided sheets were laminated in the thickness direction. A laminated sheet was thus obtained (ref: FIG. 2( c)). Then, the obtained laminated sheet was hot-pressed under the same conditions as described above with the above-described vacuum hot-press (ref: FIG. 2( a)).

Then, the obtained laminated sheet was hot-pressed under the same conditions as described above with the above-described vacuum hot-press (ref: FIG. 2( a)).

Then, a series of the above-described operations of cutting, laminating, and hot-pressing (ref: FIG. 2) was repeated four times. A thermal conductive layer (uncured state) having a thickness of 0.3 mm was thus obtained (ref: FIG. 3).

Preparation Examples 2 to 16

Thermal conductive layers (Preparation Examples 2 to 16) were obtained in the same manner as in Preparation Example 1 based on the mixing ratio and the production conditions of Tables 1 to 3 (ref: FIG. 3).

(Production of Thermal Conductive Adhesive Sheet) Production Example 1

A varnish (solvent: MEK, solid content concentration: 50 mass %, fillerless type) of acrylic pressure-sensitive adhesive was applied to the surface of a separator so that the thickness thereof when dried was 10 μm. Then, the MEK was distilled away by vacuum drying, thereby forming a pressure-sensitive adhesive layer.

Then, the pressure-sensitive adhesive layer of Preparation Example 1 was pressure bonded to the thermal conductive layer, thus producing a thermal conductive adhesive sheet (ref: FIG. 4).

Production Examples 2 to 16

Thermal conductive adhesive sheets (Production Examples 2 to 16) were obtained in the same manner as in Production Example 1, except that the thermal conductive layers of Preparation Examples 2 to 16 were used (ref: FIG. 4).

(Production of Heat Dissipation Structure) Example 1

A flat-plate substrate made of polyimide, electronic components (an IC chip having a thickness of 2 mm, a condenser having a thickness of 1 mm, a coil having a thickness of 4 mm, and a resistor having a thickness of 0.5 mm) to be mounted on the substrate, and a frame were prepared (ref: FIG. 5).

Then, the thermal conductive adhesive sheet of Production Example 1 was cut to give a size such that its center portion and one end portion overlap with the substrate, and the other end portion does not overlap with the substrate.

Then, the thermal conductive adhesive sheet and the substrate were disposed such that the center portion and one end portion of the pressure-sensitive adhesive layer face the electronic components, and then the other end portion of the thermal conductive adhesive sheet was bent upward. Thereafter, the thermal conductive adhesive sheet was pressure bonded (temporary fixed) toward the electronic components and the frame using a sponge roll made of silicone resin (ref: FIG. 9).

In this way, the center portion and one end portion of the thermal conductive adhesive sheet were adhered to the top face of the electronic components, and the other end portion of the thermal conductive adhesive sheet was adhered to the frame.

A gap was formed between the center portion and one end portion of the thermal conductive adhesive sheet and the substrate exposed from the electronic components (ref: FIG. 9).

Examples 2 to 16

Heat dissipation structures (Examples 2 to 16) were formed in the same manner as in Example 1, except that the thermal conductive adhesive sheets of Production Examples 2 to 16 described in Table 4 were used instead of the thermal conductive adhesive sheet of Production Example 1.

Example 17

A heat dissipation structure was made in the same manner as in Example 1, except that the pressure-sensitive adhesive layer was not provided in the production of the thermal conductive adhesive sheet (ref: FIG. 6).

Examples 18 to 32

Heat dissipation structures (Examples 18 to 32) were produced in the same manner as in Examples 2 to 16, except that the pressure-sensitive adhesive layer was not provided in the production of the thermal conductive adhesive sheets (ref: FIG. 6).

Evaluation 1. Thermal Conductivity

The thermal conductivity of the thermal conductive layers of Preparation Examples 1 to 16 was measured.

That is, the thermal conductivity in the plane direction (SD) was measured by a pulse heating method using a xenon flash analyzer “LFA-447” (manufactured by Erich NETZSCH GmbH & Co. Holding KG).

The results are shown in Tables 1 to 3.

2. Porosity (P)

The porosity (P1) of the thermal conductive layers before curing in Preparation Examples 1 to 16 was measured by the following method.

Measurement method of porosity: The thermal conductive sheet was cut along the thickness direction with a cross section polisher (CP); and the cross section thus appeared was observed with a scanning electron microscope (SEM) at a magnification of 200. The obtained image was binarized based on the pore portion and the non-pore portion; and the area ratio, i.e., the ratio of the pore portion area to the total area of the cross section of the thermal conductive sheet was calculated.

The results are shown in Tables 1 to 3.

3. Conformability to Irregularities (3-Point Bending Test)

The 3-point bending test in conformity with JIS K 7171 (2010) was carried out for the thermal conductive layers before curing by heat of Preparation Examples 1 to 16 with the following test conditions, thus evaluating conformability to irregularities with the following evaluation criteria. The results are shown in Tables 1 to 3.

Test Conditions:

Test piece: size 20 mm×15 mm

Distance between supporting points: 5 mm

Testing speed: 20 mm/min (indenter depressing speed)

Bending angle: 120 degrees

(Evaluation Criteria)

Excellent: No fracture was observed.

Good: Almost no fracture was observed.

Bad: Fracture was clearly observed.

4. Printed Mark Visibility (Mark Adhesion by Printing: Mark Adhesion by Inkjet Printing or Laser Printing)

Marks were printed on the thermal conductive layer of Preparation Examples 1 to 16 by inkjet printing and laser printing, and the marks were observed.

As a result, it was confirmed that the mark was excellently visible in both cases of inkjet printing and laser printing, and that mark adhesion by printing was excellent in any of the thermal conductive layers of Preparation Examples 1 to 16.

5. Volume Resistivity

The volume resistivity (R) of the thermal conductive layers in Preparation Examples 1 to 16 was measured.

That is, the volume resistivity (R) of the thermal conductive layers was measured in conformity with JIS K 6911 (testing methods for thermosetting plastics, 2006).

The results are shown in Tables 1 to 3.

6. Initial Adhesion Test 6-1. Initial Adhesion Test to Mounting Substrate for Notebook PC

Initial adhesion tests (1) and (2) of the uncured thermal conductive layers in Preparation Examples 1 to 16 to a mounting substrate for notebook PC on which a plurality of electronic components are mounted were conducted.

That is, the thermal conductive layer was temporary fixed to the surface (the side on which the electronic components are mounted) along the horizontal direction of the mounting substrate for notebook PC using a sponge roll made of silicone resin by thermocompression bonding at 80° C. (Preparation Examples 1 to 9, and Preparation Examples 11 to 16) or 120° C. (Preparation Example 10), allowed to stand for 10 minutes, and the mounting substrate for notebook PC was disposed along the up-down directions (Initial Adhesion Test (2)).

Afterwards, the mounting substrate for notebook PC was positioned so that the thermal conductive layer faces downward (that is, turned over to be upside down from the position of the temporary fixing) (Initial Adhesion Test (1)).

Then, in the above-described Initial Adhesion Test (1) and Initial Adhesion Test (2), the thermal conductive layer was evaluated based on the criteria below. The results are shown in Tables 1 to 3.

<Criteria>

Good: It was confirmed that the thermal conductive layer did not fall off from the mounting substrate for notebook PC.

Bad: It was confirmed that the thermal conductive layer fell off from the mounting substrate for notebook PC.

6-2. Initial Adhesion Test to Stainless Steel Substrate

Initial adhesion tests (1) and (2) were conducted in the same manner as described above for adhesion of the uncured thermal conductive layer of Preparation Examples 1 to 16 to a stainless steel substrate (made of SUS 304).

Then, in the above-described Initial Adhesion Test (1) and Initial Adhesion Test (2), the thermal conductive layer was evaluated based on the criteria below. The results are shown in Tables 1 to 3.

<Criteria>

Good: It was confirmed that the thermal conductive layer did not fall off from the stainless steel substrate.

Bad: It was confirmed that the thermal conductive layer fell off from the stainless steel substrate.

7. Volume Resistivity

The volume resistivity (R) of the thermal conductive layers before curing in Preparation Examples 1 to 16 was measured.

That is, the volume resistivity (R) of the thermal conductive layers was measured in conformity with JIS K 6911 (testing methods for thermosetting plastics, 2006).

The results are shown in Tables 1 to 3.

8. Heat Dissipation

The electronic components in the heat dissipation structure of Examples 1 to 32 were operated for 1 hour. As the surface temperature of the thermal conductive adhesive sheet during the operation was measured with an infrared camera, it was confirmed that the surface temperature was 70° C. and a rise in temperature was suppressed.

On the other hand, as the substrate (substrate in the heat dissipation structure of the heat dissipation structure of Comparative Example 1) in which the thermal conductive adhesive sheet was not used was evaluated in the same manner, it was confirmed that the temperature right above the electronic component was 130° C.

Thus, it was confirmed that heat dissipation of the heat dissipation structure of Examples 1 to 32 was excellent.

TABLE 1 Preparation Example Prepa- Prepa- Prepa- Prepa- Prepa- Prepa- ration ration ration ration ration ration Average Particle Exam- Exam- Exam- Exam- Exam- Exam- Size (μm) ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 Mixing Boron PT-110^(*1) 45 13.42 3.83 5.75 12.22 23 — Formula- Nitride [70] [40]   [50]   [68]   [80]   tion of Parti- [69] [38.8] [48.8] [66.9] [79.2] Compo- cle/g^(*A)/ UHP-1^(*2) 9 — — — — — 12.22 nents [vol %]^(*B)/ [68]   [vol %]^(*C) [66.9] Polymer Thermo- Epoxy Epoxy Resin A^(*3) — 3 3 3 3 3 setting Resin (Semi-solid) Resin Composi- Epoxy Resin B^(*4) 1 — — — — — tion (Liquid) Epoxy Resin C^(*5) — — — — — — (Solid) Epoxy Resin D^(*6) 2 — — — — — (Solid) Curing Agent^(*7) — 3 3 3 3 3 (Solid Content in (0.15) (0.15) (0.15) (0.15) (0.15) Grams) Curing Agent^(*8) 3 — — — — — (Solid Content in (0.15) Grams) Thermo- Polyethylene*⁹ — — — — — — plastic Produc- Hot- Temperature(° C.) 80 80 80 80 80 80 tion Con- pressing Number of Time (Times)^(*D) 5 5 5 5 5 5 ditions Load (MPa)/(tons) 20/5 20/5 20/5 20/5 20/5 20/5 Evalua- Thermal Thermal Conductivity Plane Direction(SD) 30 4.5 6.0 30.0 32.5 17.0 tion Conduc- (W/m · K) Thickness 2.0 1.3 3.3 5.0 5.5 5.8 tive Direction(TD) Layer Ratio(SD/TD) 15.0 3.5 1.8 6.0 5.9 2.9 Porosity (vol %) 4 0 0 5 12 6 Conformability to Irregularities/ Excellent Good Good Good Good Good 3-point bending test JIS K 7171(2008) Volume Resistivity(Ω · cm) 2 × 10¹⁴ 5.5 × 10¹⁴ 3.4 × 10¹⁴ 2.1 × 10¹⁴ 1.3 × 10¹⁴ 1.7 × 10¹⁴ JIS K 6911 (2006 Initial Adhesion To Test (1) Good Good Good Good Good Good Test Mounting Substrate for Test (2) Good Good Good Good Good Good Notebook PC To Test (1) Good Good Good Good Good Good Stainless Steel Test (2) Good Good Good Good Good Good Substrate Boron Orientation Angle (α)(degrees) 12 18 18 15 13 20 Nitride Particles g^(*A): Blended Weight [vol %]^(*B): Percentage relative to the total volume of the thermal conductive sheet (excluding curing agent) [vol %]^(*C): Percentage relative to the total volume of the thermal conductive sheet Number of Time^(*D): Number of times of hot-pressing of laminated sheet

TABLE 2 Preparation Example Prepa- Prepa- Prepa- Prepa- Prepa- Average ration ration ration ration ration Particle Example Example Example Example Example Size (μm) 7 8 9 10 11 Mixing For- Boron PT-110^(*1) 45 12.22 12.22 12.22 3.83 13.42 mulation Nitride [68]   [68]   [68]   [60] [60] of Com- Parti- [66.9] [66.9] [66.9] [60] [69] ponents cle/g^(*A)/ UHP-1^(*2) 9 — — — — — [vol %]^(*B)/ [vol %]^(*C) Polymer Thermo- Epoxy Epoxy Resin A^(*3) — — — — — setting Resin (Semi-solid) Resin Composi- Epoxy Resin B^(*4) 1.5 3 — — — tion (Liquid) Epoxy Resin C^(*5) 1.5 — 3 — — (Solid) Epoxy Resin D^(*6) — — — — 3 (Solid) Curing Agent^(*7) 3 3 3 — 3 (Solid Content in (0.15) (0.15) (0.15) (0.15) Grams) Curing Agent^(*8) — — — — — (Solid Content in Grams) Thermo- Polyethylene*⁹ — — — 1 — plastic Resin Produc- Hot- Temperature(° C.) 80 80 80 120 80 tion Condi- pressing Number of Time (Times)^(*D) 5 5 5 5 5 tions Load (MPa)/(tons) 20/5 20/5 20/5 4/1 20/5 Evaluation Thermal Thermal Conductivity Plane Direction(SD) 30.0 30.0 30.0 20 24.5 Conduc- (W/m · K) Thickness 5.0 5.0 5.0 2.0 2.1 tive Direction(TD) Layer Ratio(SD/TD) 6.0 6.0 6.0 10.0 11.7 Porosity (vol %) 6 6 5 8 5 Conformability to Irregularities/ Good Good Bad Bad Bad 3-point bending test JIS K 7171(2008) Volume Resistivity(Ω · cm) 2.2 × 10¹⁴ 2.4 × 10¹⁴ 1.1 × 10¹⁴ 4.1 × 10¹⁴ 1.3 × 10¹⁴ JIS K 6911 (2006) Initial Adhesion To Test (1) Good Good Good Good Good Test Mounting Substrate for Test (2) Good Good Good Good Good Notebook PC To Test (1) Good Good Good Good Good Stainless Steel Test (2) Good Good Good Good Good Substrate Boron Orientation Angle (α)(degrees) 15 16 16 15 16 Nitride Particles g^(*A): Blended Weight [vol %]^(*B): Percentage relative to the total volume of the thermal conductive sheet (excluding curing agent) [vol %]^(*C): Percentage relative to the total volume of the thermal conductive sheet Number of Time^(*D): Number of times of hot-pressing of laminated sheet

TABLE 3 Preparation Example Prepa- Prepa- Prepa- Prepa- Prepa- Average ration ration ration ration ration Particle Example Example Example Example Example Size (μm) 12 13 14 15 16 Mixing For- Boron PT-110^(*1) 45 3.83 13.42 13.42 13.42 13.42 mulation Nitride [40]   [70] [70] [70] [70] of Com- Particle/g^(*A)/ [37.7] [69] [69] [69] [69] ponents [vol %]^(*B)/ UHP-1^(*2) 9 — — — — — [vol %]^(*C) Polymer Thermo- Epoxy Epoxy Resin A^(*3) 3 3 3 3 3 setting Resin (Semi-solid) Resin Composi- Epoxy Resin B^(*4) — — — — — tion (Liquid) Epoxy Resin C^(*5) (Solid) Epoxy Resin D^(*6) — — — — — (Solid) Curing Agent^(*7) 6 3 3 3 3 (Solid Content in (0.3) (0.15) (0.15) (0.15) (0.15) Grams) Curing Agent^(*8) — — — — — (Solid Content in Grams) Thermo- Polyethylene*⁹ — — — — — plastic Resin Produc- Hot- Temperature(° C.) 80 60 70 80 80 tion Condi- pressing Number of Time (Times)^(*D) 5 5 5 5 5 tions Load (MPa)/(tons) 20/5 20/5 20/5 20/5 40/10 Evaluation Thermal Thermal Conductivity Plane Direction(SD) 4.1 10.5 11.2 32.5 50.7 Conductive (W/m · K) Thickness 1.1 2.2 3.0 5.5 7.3 Layer Direction(TD) Ratio(SD/TD) 3.7 4.8 3.7 5.9 6.9 Porosity (vol %) 0 29 26 8 3 Conformability to Irregularities/ Excellent Excellent Excellent Excellent Good 3-point bending test JIS K 7171(2008) Volume Resistivity(Ω · cm) 6.4 × 10¹⁴ 0.6 × 10¹⁴ 0.8 × 10¹⁴ 2.5 × 10¹⁴ 5.3 × 10¹⁴ JIS K 6911 (2006 Initial Adhesion To Test (1) Good Good Good Good Good Test Mounting Substrate for Test (2) Good Good Good Good Good Notebook PC To Test (1) Good Good Good Good Good Stainless Steel Test (2) Good Good Good Good Good Substrate Boron Orientation Angle (α)(degrees) 20 17 15 15 13 Nitride Particles g^(*A): Blended Weight [vol %]^(*B): Percentage relative to the total volume of the thermal conductive sheet (excluding curing agent) [vol %]^(*C): Percentage relative to the total volume of the thermal conductive sheet Number of Time^(*D): Number of times of hot-pressing of laminated sheet

TABLE 4 Pressure- Heat Sensitive Dissipation Thermal Conductive Thermal Conductive Adhesive Structure Adhesive Sheet Layer Layer Example 1 Production Example 1 Preparation Example 1 Present Example 2 Production Example 2 Preparation Example 2 Example 3 Production Example 3 Preparation Example 3 Example 4 Production Example 4 Preparation Example 4 Example 5 Production Example 5 Preparation Example 5 Example 6 Production Example 6 Preparation Example 6 Example 7 Production Example 7 Preparation Example 7 Example 8 Production Example 8 Preparation Example 8 Example 9 Production Example 9 Preparation Example 9 Example 10 Production Example 10 Preparation Example 10 Example 11 Production Example 11 Preparation Example 11 Example 12 Production Example 12 Preparation Example 12 Example 13 Production Example 13 Preparation Example 13 Example 14 Production Example 14 Preparation Example 14 Example 15 Production Example 15 Preparation Example 15 Example 16 Production Example 16 Preparation Example 16 Example 17 Production Example 17 Preparation Example 1 Absent Example 18 Production Example 18 Preparation Example 2 Example 19 Production Example 19 Preparation Example 3 Example 20 Production Example 20 Preparation Example 4 Example 21 Production Example 21 Preparation Example 5 Example 22 Production Example 22 Preparation Example 6 Example 23 Production Example 23 Preparation Example 7 Example 24 Production Example 24 Preparation Example 8 Example 25 Production Example 25 Preparation Example 9 Example 26 Production Example 26 Preparation Example 10 Example 27 Production Example 27 Preparation Example 11 Example 28 Production Example 28 Preparation Example 12 Example 29 Production Example 29 Preparation Example 13 Example 30 Production Example 30 Preparation Example 14 Example 31 Production Example 31 Preparation Example 15 Example 32 Production Example 32 Preparation Example 16

In Tables 1 to 3, values for the components are in grams unless otherwise specified.

In the rows of “boron nitride particles” in Tables 1 to 3, values on the top represent the blended weight (g) of the boron nitride particles; values in the middle represent the volume percentage (vol %) of the boron nitride particles relative to the total volume of the solid content excluding the curing agent in the thermal conductive sheet (that is, solid content of the boron nitride particles, and epoxy resin or polyethylene); and values at the bottom represent the volume percentage (vol %) of the boron nitride particles relative to the total volume of the solid content in the thermal conductive sheet (that is, solid content of boron nitride particles, epoxy resin, and curing agent).

For the components with “*” added in Tables 1 to 3, details are given below.

-   PT-110*¹: trade name, plate-like boron nitride particles, average     particle size (light scattering method) 45 μm, manufactured by     Momentive Performance Materials Inc. -   UHP-1*²: trade name: SHOBN®UHP-1, plate-like boron nitride     particles, average particle size (light scattering method) 9 μm,     manufactured by Showa Denko K.K. -   Epoxy Resin A*³: OGSOL EG (trade name), bisarylfluorene epoxy resin,     semi-solid, epoxy equivalent 294 g/eqiv., softening temperature     (ring and ball test) 47° C., melt viscosity (80° C.) 1360 mPa·s,     manufactured by Osaka Gas Chemicals Co., Ltd. -   Epoxy Resin B*⁴: jER® 828 (trade name), bisphenol A epoxy resin,     liquid, epoxy equivalent 184 to 194 g/eqiv., softening temperature     (ring and ball test) below 25° C., melt viscosity (80° C.) 70 mPa·s,     manufactured by Japan Epoxy Resins Co., Ltd. -   Epoxy Resin C^(*5): jER® 1002 (trade name), bisphenol A epoxy resin,     solid, epoxy equivalent 600 to 700 g/eqiv., softening temperature     (ring and ball test) 78° C., melt viscosity (80° C.) 10000 mPa·s or     more (measurement limit or more), manufactured by Japan Epoxy Resins     Co., Ltd. -   Epoxy Resin D*⁶: EPPN-501HY (trade name), triphenylmethane epoxy     resin, solid, epoxy equivalent 163 to 175 g/eqiv., softening     temperature (ring and ball test) 57 to 63° C., manufactured by     NIPPON KAYAKU Co., Ltd. -   Curing Agent*⁷: a solution of 5 mass % Curezol® 2PZ (trade name,     manufactured by Shikoku Chemicals Corporation) in methyl ethyl     ketone. -   Curing Agent*⁸: a dispersion of 5 mass % Curezol® 2P4MHZ-PW (trade     name, manufactured by Shikoku Chemicals Corporation) in methyl ethyl     ketone. -   Polyethylene*⁹: low density polyethylene, weight average molecular     weight (Mw) 4000, number average molecular weight (Mn) 1700,     manufactured by Sigma-Aldrich Co.

While the illustrative embodiments of the present invention are provided in the above description, such is for illustrative purpose only and it is not to be construed as limiting the scope of the present invention. Modification and variation of the present invention that will be obvious to those skilled in the art is to be covered by the following claims. 

1. A heat dissipation structure comprising: a substrate, an electronic component mounted on the substrate, a heat dissipation member for dissipating heat generated from the electronic component, and a thermal conductive adhesive sheet provided on the substrate so as to cover the electronic component, wherein the thermal conductive adhesive sheet includes a thermal conductive layer containing a plate-like boron nitride particle, the thermal conductive layer has a thermal conductivity in a direction perpendicular to the thickness direction of the thermal conductive layer of 4 W/m·K or more, and the thermal conductive adhesive sheet is in contact with the heat dissipation member.
 2. The heat dissipation structure according to claim 1, wherein the thermal conductive adhesive sheet includes an adhesive layer or a pressure-sensitive adhesive layer laminated onto at least one face of the thermal conductive layer, and the adhesive layer or the pressure-sensitive adhesive layer is adhered to or pressure-sensitively adhered to the substrate. 